In lenticular type three-dimensional (3-D) photography, a plurality of two-dimensional (2-D) views of the scene are taken from a number of horizontally spaced vantage points and a series of 2-D images is then compressed and printed at the focal plane on the emulsion of each of the lenticules of the lenticular print film to form a 3-D composite image of the scene.
When a person is viewing a 3-D photograph, the right and left eyes see two image bands which form a stereo pair. The spatial parallax between the images of the stereo pair reconstructs the spatial effect and the sensation of depth to the photographed scene.
The method of taking and composing lenticular type 3-D photographs is explained in some of the following publications.
N. A. Valyus in Stereoscopy (The Focal Press 1962) at pages 195-205 discloses the basic method of taking and printing 3-D photographs on lenticular print material.
Rudolf Kingslake in Applied Optics and Optical Engineering (Academic Press 1965) at pages 108-116 also discusses some of the basic principles involved in lenticular three-dimensional photography.
Takanori Okoshi in Three-Dimensional Imaging Technique (Academic Press 1972) at pages 61-95 discusses a number of techniques for taking three-dimensional photographs.
The following U.S. Pat. Nos. are of interest in connection with three-dimensional photographic techniques.
3,895,867 (Lo et al) PA1 4,059,354 (Lo et al) PA1 4,101,210 (Lo et al) PA1 4,132,468 (Lo et al) PA1 4,468,115 (Lo et al) PA1 4,120,562 (Lo et al) PA1 3,482,913 (Glenn) PA1 3,518,920 (Glenn)
In the composing of a lenticular type 3-D photograph, a plurality of 2-D negative views is simultaneously or sequentially projected through the lenticules of the 3-D print material to form groups of image elements of the 2-D negative view, each representing a different view of the photographic object. Each of the 2-D negative views is projected through a different angle of projection on to the 3-D print material. The total angle of projection is dependent upon the acceptance angle of the lenticule of the print material. Therefore each of the 2-D negative views is positioned at a different location in the field of the enlarging lens. Some of the negative views are positioned near the center of the field of the enlarging lens and some are positioned near the edge.
Due to the vignetting effect of the enlarging lens, the illumination is brighter at the center of the field and gradually decreases towards the edge of the field of the lens. Consequently the area of the 2-D negative views projected at the center of the field will receive maximum illumination and produce image bands of high density while the area of the 2-D negative views projected near the edge of the field will receive minimal illumination and produce image elements of lower density.
In the printing of 3-D photographs, there are plurality of image bands (corresponding to the total number of 2-D views) under each lenticule. In each image band a single or multiple condensed image element from a particular 2-D view is printed. If the width of the image element is smaller than the width of the image band, then the same 2-D view will be repeat printed several times so that each image band is formed by several image elements in order to fill the full width of the image band and not leave any unexposed spaces. Each of the image elements is exposed from a different angle of projection (to avoid overlapping of the image elements), which results in the image element exposed near the center of the field of the enlarging lens receiving more illumination than image elements toward the edge.
Since the image bands are generally made up of image elements which are exposed through different angles of the lenticules of the print material, the vignetting effect of the lenticules itself should also be compensated for in addition to the vignetting effect of the enlarging lens.
The vignetting of the enlarging lens and the lenticules of the print material results in density differences and also in color off balance between the image elements depending upon the angle of projection as some parts of the emulsion layer the lenticules are overexposed and other parts are underexposed. Differences in density and color balance are particularly acute when viewing a stereoscopic pair of images. This results in the observed phenomenon of the 3-D picture appearing to flicker when viewed from different viewing angles which makes the picture uncomfortable to view. The variations in density and color between each enlarged 2-d view is disconcerting to a viewer. The overall quality of the picture is decreased because the left and right eye each view an image of different density.